Metal-organo compounds with sterically exposed metal-metal bonds, and a method for their production

ABSTRACT

Metal-organo complex characterized as having at least one sterically exposed metal-metal bond, and having the structure: 
     
         R.sub.n M  M&#39;R.sub.n 
    
     wherein R represents a ligand which may contain one or more atoms of carbon, hydrogen, oxygen, nitrogen, sulfur or phosphorus; n is an integer of from 1 to 3; M and M&#39; each represent the same or a different transition metal; and the symbol   represents at least one sterically exposed metal-metal bond. 
     The preparative method involves the low temperature reaction between an alkali metal naphthalene in an ethereal solvent, with the dihalogenide of at least one metal-organic species. The reaction mixture is allowed to slowly warm to ambient temperatures, the solvent is evaporated, and the naphthalene sublimed at temperatures below 40° C. The remaining crude product is extracted with an organic solvent, the extract is separated from the insoluble portion, and the product recovered by evaporating the solvent. 
     The metal-organo complex has utility as an absorbent of nitrogen when present as a contaminant in argon. .Iadd. 
     When M and M&#39; in the above formula are both titanium, and R is cyclopentadienyl, and n is 2 the above preparative method results in a metal-organo complex, as above defined, wherein pairs of the ligands are pi-bonded to each titanium atom, and one of these four ligands bridges the two titanium atoms by a pi-bond to one titanium and a sigma-bond to the other. .Iaddend.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates to a metal-organo complex having at least onesterically exposed metal-metal bond, .[.and having.]. .Iadd.hereinrepresented by .Iaddend.the structure:

    R.sub.n M  M'R.sub.n

wherein R represents a ligand which contains one or more atoms ofcarbon, hydrogen, oxygen, nitrogen, sulfur or phosphorus; n is aninteger of from 1 to 3; M and M' each represent the same or a differenttransition metal; and the symbol

represents at least one sterically exposed metal-metal bond.

This invention also relates to a method of synthesizing the abovemetal-organo complex.

II. Description of the Prior Art

In the early nineteen fifties a new class of organo metallic compoundswas discovered, starting with dicyclopentadienyl iron or "ferrocene."Analogous compounds were seen prepared, similarly complexing a greatmany of the transition metals. Particular attention was focused on thetitanium complex, reported to be dicyclopentadienyl titanium, and alsoreferred to as "titanocene." At first this was thought to be a simple"sandwich" configuration, its essential structure being the symmetricalbinding of the central metal atom to all five carbon atoms of eachcyclopentadienyl ring.

In the mid sixties, it was found and confirmed that the materialreported to be dicyclopentadienyl titanium was actually a dimer.

By 1970, it was reported (H. H. Brintzinger and J. E. Bercaw, JACS 92:21pp. 6182-6185) that the metal-organo complex which various investigatorshad isolated, was not [(C₅ H₅)₂ Ti]₂ as had been erroneously reported,but its stable isomer, the hydride, [(C₅ H₅)(C₅ H₄)TiH]₂.

SUMMARY OF THE INVENTION

I have now found .[.that.]. .Iadd.a compound closely related to.Iaddend.the true bis(dicyclopentadienyl titanium II), .[.[(C₅ H₅)₂Li]₂, is a very active metastable isomer,.]. .Iadd.and having theformula (C₅ H₅)₃ Ti₂ (C₅ H₄) .Iaddend.which, by the employment of theprocess of .[.our.]. .Iadd.my .Iaddend.invention, can be isolated. It ismuch more active than the more stable hydride, [(C₅ H₅ )(C₅ H₄)TiH]₂ towhich .[.isomer.]. it spontaneously reverts on heating. .Iadd.Thestructure appears to be an attachment of pairs of cyclopentadienylradicals by "pi" bonds to each of the titanium atoms with one of theseradicals bridging the two titanium atoms by a "pi" bond to one titaniumatom and by a "sigma" bond to the other titanium atom. .Iaddend.

.[. Bis(dicyclopentadienyl titanium II).]. .Iadd.The above describedtitanium complex .Iaddend.and the .[.analogous.]. complexes of severalother transition metals .Iadd.obtained by my preparative method.Iaddend.have at least one metal-metal sterically exposed bond. Thesebonds are responsible for the high degree of reactivity of therespective complexes toward small molecules such as hydrogen, nitrogen,carbon monoxide and aromatic hydrocarbons.

The preparative method of my invention may be applied to the productionof .[.bis(dicyclopentadienyl titanium II).]. .Iadd.the above describedtitanium complex .Iaddend.as well as to .[.analogous.]. dimers havingvarious ligands and similar or dissimilar transition metals with eithersingle or multiple sterically exposed metal-metal bonds. The method ofthe present invention comprises a low temperature reduction of (R)₂ MX₂,or a mixture of (R)₂ MX₂ and (R₂)M'X₂ in an ethereal solvent where Rrepresents the selected ligand; M a transition metal; M' a secondtransition metal, and X a halogen.

The preparative method may briefly be stated as follows:

An alkali metal naphthalene, generally prepared in situ, but prior tothe addition of the dihalogenide which will furnish the ligands, isallowed to react in an ethereal solvent, in an inert atmosphere, and attemperatures below about -35° C. with the dihalogenide of at least onemetal-organic species. The reaction mixture is allowed to gradually warmto ambient temperatures, the solvent is evaporated, and the naphthalenesublimed, both operations being carried out under reduced pressure, andat temperatures below 40° C. The residue obtained is extracted with anorganic solvent, or a mixture of solvents, and the product metal-organocomplex obtained by removal of the solvent. The highly active productmust be protected from oxygen, and if wet with solvent, it must also beprotected from nitrogen, with which it will then react.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

When reference is made herein to "transition metals," those metals arereferred to in which an inner electron shell rather than an outer shellis partially filled. In the periodic table, those metals, the atoms ofwhich are so structured, include elements 21 through 30 (scandiumthrough zinc), 39 through 48 (yttrium through cadmium), 57 through 80(lanthanum through mercury) and 80 through 103 (actinium throughlawrencium).

When reference is made to "sterically expose metal-metal bonds," thosemetal-metal bonds are specified wherein the molecules have a spatialarrangement of their atoms such that the bond is readily available toanother molecule with which it can react. There are not adjacent atomicstructures to partially block or hinder a reaction.

When reference is made to a "ligand," we refer herein to those organicmolecules, atoms or ions which are attached to one or the other of themetallic atoms designated herein as M and M' .Iadd.by "sigma" or "pi"bonds as in the subject complexes, especially cyclopentadienyl andpinacolate. .Iaddend.

.[.The method of the present invention may be employed to produce suchnovel metal-organo compounds having metal-metal bonds, asbis(dicyclopentadienyl titanium II), bis(zirconium II pinacolate) andother analogous compounds having other transition metals and otherligands than the cyclopentadienyl and the pinacolate structures..].

In carrying out the method, an alkali metal, such as potassium, sodiumor lithium is stirred with at least the stoichiometric amount ofnaphthalene in a substantially dry, oxygen-free ethereal solvent such astetrahydrofuran (THF) or dimethyl ether. The operation is carried out ina reaction vessel from which the air or oxygen has been removed, orreplaced with an inert atmosphere. Stirring is continued at aboutambient temperature until the formation of the metal-naphthalene or"naphthalide" solution is essentially complete, and no appreciablequantity of the elemental alkali metal remains.

The solution is now cooled to a temperature within the range of -200° C.to -35° C., preferably between -200 and -150° C., and approximately thestoichiometric quantity of the dihalogenide of at least onemetal-organic species such as (C₅ H₅)₂ TiCl₂ (dicyclopentadienyltitanium dichloride) [(CH₃)₂ CO]₂ ZrCl₂ (dichlorozirconium pinacolate)or (C₅ H₅)₂ MoBr₂ (dicyclopentadienyl molybdenum dibromide) are added.Additional ethereal solvent is generally added at this point. Althoughnot essential to the process, it serves to rinse the last of the chargeof solid dihalogenide into the reactor.

The temperature is next raised to, and maintained within the range of-100 and -35° C., preferably between -90 and -70° C., for from 2 to 60hours, preferably from 30 to 50 hours. Following this, the temperatureis raised to and maintained between -55 to -25° C., preferably withinthe range of -50 to -40° C. for between 2 to 30 hours, preferablybetween 10 and 25 hours, then allowed to warm to ambient temperaturesover a period of from 1 to 60 hours, preferably from 30 to 50 hours.This slow warming period, as well as the low temperatures employedduring the reaction are features of the present invention. If preparedat ambient temperatures an inordinate amount of the .[.isomeric.].hydride, .Iadd.[(C₅ H₅)(C₅ H₄)TiH]₂, .Iaddend.would be produced; and ifthe batch were rapidly warmed to ambient temperatures, the product yieldwould be adversely affected.

The ethereal solvent and naphthalene are next removed by distillationand sublimation in a system, from which the gaseous atmosphere has beenevacuated, at temperatures below 40° C., preferably between 25 and 35°C. The remaining crude residue is solvent extracted at temperaturesbetween .Iadd.minus .Iaddend.95° C. and ambient temperature, preferablybetween -90 and -70° C. to obtain the product. A product assaying atleast 80% can be obtained by the above procedure.

This product can be brought to a purity of better than 96% by additionalsolvent extractions.

The organic extraction solvents may be aliphatic or aromatichydrocarbons, or a mixture of both. Benzene and toluene are effective,but toluene is preferred because benzene solidifies at 5.5° C., and cantherefore, be employed only when the extractions are carried out aboveits freezing point.

Since toluene displays a certain affinity for these products, it ispreferred that an aliphatic hydrocarbon having a higher boiling pointthan toluene, and displaying substantially no affinity for the product,such as octane, be added to the extract before it is taken to dryness.With this modification, the toluene, having a lower boiling point, isremoved first, and a dry, free-flowing product is thereby obtained.There are, of course, many suitable combinations of solvents which bearthis desired relationship.

In preparing .[.bis(dicyclopentadienyl titanium II).]. .Iadd.the abovedescribed titanium complex with cyclopentadienyl ligands .Iaddend.by theabove procedure, it is found that this product has considerably greatersolubility in toluene, which is the preferred solvent, than does theless reactive .[.isomeric.]. hydride [(C₅ H₅)(C₅ H₄)TiH]₂, which ispresent as a contaminant.

The following examples, in which parts are by weight, are illustrativeof the novel compounds prepared, and of the method of this inventionwhich is employed in their preparation.

EXAMPLE 1

Five parts by weight of elemental potassium and 18 parts of naphthaleneare charged into an agitated jacketed vessel, under an argon atmosphere.178 parts of dry, oxygen-free tetrahydrofuran (THF), are distilleddirectly into the vessel, and the mixture is agitated at 20° C. for 24hours, after which period the potassium naphthalene solution is completewith no unreacted potassium metal remaining. The solution is now cooledto -196° C. and 15.3 parts of solid dicyclopentadienyl titaniumdichloride are added, together with 300 parts of additional THF. All airis evacuated from the system, and agitation is maintained throughout theoperation.

The mixture is now warmed to -80° C. and maintained at this temperaturewith agitation for 48 hours. Next, the temperature is raised to andmaintained at -45° C. for 24 hours with agitation. The reaction mixtureis then allowed to warm slowly to room temperature with agitation, overa period of 48 hours.

The THF is next distilled off in the absence of air or any gaseousatmosphere at a temperature of 20° C., and subsequently the naphthaleneis removed by sublimation under vacuum at a temperature of 35° C. Theremaining material is a dry, green to black crude product.

The dark product obtained is now twice extracted at -80° C., each timewith 173 parts of toluene. The combined, filtered extracts areevaporated under vacuum at ambient temperature to one quarter of theoriginal combined volume, and 70 parts of octane are added to theconcentrated extract with agitation. The extract is now evaporated todryness under vacuum at ambient temperature. Throughout theseconcentrations and evaporations, great care is exercised to exclude air(both oxygen and nitrogen) from the system.

Since the toluene has the lower boiling point of the two solventsemployed, it is first removed, leaving the product as a slurry inoctane. In order to insure that all the toluene is displaced, a second70 parts of octane are added, then the slurry is taken to dryness undervacuum at ambient temperature. The product is found to contain 81%.[.bis(dicyclopentadienyl titanium II).]. .Iadd.of the subject titaniumcomplex having cyclopentadienyl radicals. .Iaddend.Subsequently, theassay is brought to 96% by re-extracting the product with toluene.

.Iadd.This product "A" can be further purified by crystallization fromtetrahydrofuran ("THF") at controlled temperature by controlled additionof a poor solvent such as hexane. Examination of a single crystal of theresulting product "B" by X-ray diffraction, together with the infraredspectrogram of the compound, indicates the formula: .Iadd.##STR1##.Iaddend. (i.e., two titanium atoms linked by a stericallyexposed metal-metal bond, with three pi-bonded cyclopentadienyl(C₅ H₅)radicals and one bridging (σ,π) cyclopentadienyl (C₅ H₄) radical linkedto one titanium atom by a sigma bond and to the other by a pi bond; andcontaining a coordinated THF molecule and a loosely associated THFmolecule. When this tetrahydrofuran adduct "B" is dissolved in n-octaneand the solution is evaporated to dryness, a gray-black solid "C" isobtained as the residue. Its infrared spectrum, powder X-ray diffractionpattern and proton nuclear magnetic resonance spectrum are the same asthose of product "A"; the infrared spectrum shows that products "A" and"C" (which are believed to be identical) contain no tetrahydrofuran. Itis believed that the structural formula of this product is: .Iadd.##STR2##.Iaddend.

The infrared spectrum characteristic of the solvent-free product of theabove procedures, i.e. products "A" and "C" above, is represented by theupper curve in the accompanying drawing. The lower curve represents theinfrared spectrum of the crystalline product containing tetrahydrofuranadduct, i.e. the product identified as "B" above. In the drawing, theasterisks mark bonds due to n-hexadecane-d₃₄ (i.e. deuteratedn-hexadecane) used for preparing the mulls on which the spectra weretaken.

The Table below shows Debye-Scherrer X-ray diffraction data (Braggspacing, D, in Angstroms and relative intensity I/I₁ of diffracted beamvs. major line normalized to 100) taken on the above product "C".

DEBYE-SCHERRER X-RAY DIFFRACTION DATA ON PURE (C₅ H₅)₃ (C₅ H₄)Ti₂ ASPREPARED FROM CRYSTALLINE (C₅ H₅)₃ (C₅ H₄)Ti₂ (C₄ H₈ O).C₄ H₈ O 5 5 5 4

                  TABLE                                                           ______________________________________                                                D(A)°       I/I.sub. 1                                         ______________________________________                                                7.25               40                                                         6.57               13                                                         6.18               100                                                        5.62               4                                                          5.26               18                                                         5.14               15                                                         4.86               9                                                          4.58               24                                                         4.39               32                                                         4.28               8                                                          3.94               22                                                         3.61               4                                                          3.41               6                                                          2.97               3                                                          2.55               8                                                          2.49               13                                                         2.35               5                                                          2.28               6                                                          2.23               13                                                         2.09               12                                                         1.93               10                                                 ______________________________________                                    

The product .[.is identified as the true bis(dicyclopentadienyl titaniumII) by its infrared spectrum, its reaction.]. .Iadd.reacts .Iaddend.withmolecular nitrogen, .[.the substantially quantitative isomericrearrangement of the product.]. .Iadd.and partially converts over.Iaddend.to the hydride [(C₅ H₅)(C₅ H₄)TiH]₂ after prolonged heating at100° C. .[., its elemental analysis, and its molecular weightdetermination..].

EXAMPLE 2

Three parts by weight of elemental sodium and 18 parts of naphthaleneare charged into an agitated jacketed vessel under an argon atmosphere.178 parts of dry, oxygen-free liquified dimethyl ether are distilleddirectly into the vessel, and the mixture is agitated at 20° C. for 24hours, after which period the sodium naphthalene solution is completewith no unreacted sodium metal remaining. The solution is now cooled to-196° C. and 24 parts of solid zirconium dibromo pinacolate are added,together with 300 parts of additional liquid dimethyl ether. All air isevacuated from the system, and agitation is maintained throughout theoperation.

The mixture is now warmed to -80° C. and maintained at this temperaturewith agitation for 48 hours. Next, the temperature is raised to andmaintained at -45° C. for 24 hours with agitation. The reaction mixtureis then allowed to warm slowly to room temperature with agitation over aperiod of 48 hours, and the volatile dimethyl ether distills off. Thenaphthalene is sublimed at 35° C. under vacuum. The remaining residue isextracted with toluene at -80° C. in the same manner as in Example 1.

The product is identified as containing bis(zirconium II pinacolate).

EXAMPLE 3

One part by weight of elemental lithium and 19 parts of naphthalene arecharged into an agitated jacketed vessel under an argon atmosphere. 178parts of dry, oxygen-free THF are distilled directly into the vessel,and the mixture is agitated at 20° C. for 24 hours, after which periodthe lithium naphthalene solution is complete with no unreacted lithiummetal remaining. The solution is now cooled to -196° C. and 27 parts ofsolid dicyclopentadienyl hafnium dichloride are added, together with 300parts of additional THF. All air is evacuated from the system, andagitation is maintained throughout the operation. From this point on,the procedure is identical to that of Example 1, the same temperatures,period of agitation and method of isolating the final product byextraction being used.

The product is identified as containing bis(dicyclopentadienyl hafniumII).

It is apparent that many different embodiments can be made in thisinvention without departing from the spirit and scope thereof.Therefore, it is intended to be limited only as indicated in theappended claims.

I claim: .[.1. A metal-organo complex having at least one stericallyexposed metal-metal bond and having the structure: are both hafnium andR is the cyclopentadienyl ligand..]. .[.11. A method for preparing ametal-organo complex having at least one sterically exposed metal-metalbond having the structure:

    R.sub.n M  M'R.sub.n

wherein R represents the cyclopentadienyl ligand; n is an integer offrom 1 to 3; M and M' each represent the same or a different transitionmetal selected from the group consisting of titanium, zirconium,hafnium, molybdenum and tungsten; and the symbol represents a single ormultiple, sterically exposed metal-metal bond, which comprises: (a)admixing a halogenide of the metal-organo compound selected to supplythe desired ligand, with a cold ethereal solvent solution of potassium,sodium or lithium naphthalene at a temperature between -200° C. and -25°C. and agitating the mixture for at least 2 hours; (b) gradually warmingthe reaction mixture during a period of at least two hours tosubstantially ambient temperature; (c) removing the ethereal solvent andexcess naphthalene at temperatures under 40° C; and (d) extracting theresidue at a temperature not exceeding 40° C. to obtain the metal-organocomplex..].
 12. The method of claim .[.11.]. .Iadd.27 .Iaddend.whereinthe sodium, potassium or lithium naphthalene is prepared in situ, in theethereal solvent, by agitating the elemental metal and the naphthalenein said solvent as a reaction medium, prior to the addition of thehalogenide.
 13. The method of claim .[.11.]. .Iadd.27 .Iaddend.whereinboth M and M' are titanium.
 14. The method of claim .[.11.]. .Iadd.27.Iaddend.wherein both M and M' are zirconium.
 15. The method of claim.[.11.]. .Iadd.27 .Iaddend.wherein both M and M' are hafnium.
 16. Themethod of claim .[.11.]. .Iadd.27 .Iaddend.wherein both M and M' aretungsten.
 17. The method of claim .[.11.]. .Iadd.27 .Iaddend.whereinboth M and M' are molybdenum.
 18. The method of claim .[.11.]. .Iadd.27.Iaddend.wherein M is titanium and M' is molybdenum. The method of claim.[.11.]. .Iadd.27 .Iaddend.wherein the mixing of the halogenide of themetal-organo compound selected to supply the desired ligand, with thecold ethereal solvent solution of potassium, sodium or lithiumnaphthalene, is effected at a temperature of -200° C. to -150° C., andthe mixture is agitated at a temperature of between -100° C. and -35° C.for a period of between 2 and 60 hours, then at a temperature between-55° C. and -25° C. for a period of between 2 and 30 hours, and then isallowed to warm to ambient temperature over a period of from 1 to 60hours.
 20. The method of claim 19 wherein the mixture is agitated at atemperature of between -90° C. and -70° C. for a period of between 30 to50 hours, then at a temperature of between -50° C. and -40° C. for aperiod of between 10 and 25 hours, and then is allowed to warm toambient temperature over a period of from 30 to 50 hours.
 21. The methodof claim .[.11.]. .Iadd.27 .Iaddend.wherein the ethereal solvent isselected from the group consisting of tetrahydrofuran, dimethyl ether,and 1,2-dimethoxyethane.
 22. The method of claim .[.11.]. .Iadd.27.Iaddend.wherein the residue is extracted with an aromatic hydrocarbonat a temperature below -35° C., is separated from any remaininginsoluble matter, and is at least partially concentrated.
 23. The methodof claim 21 wherein a quantity of a volatile aliphatic hydrocarbon forwhich the product has less affinity than for the chosen aromatichydrocarbon solvent, and which has a higher boiling point than thechosen aromatic solvent, is added to the partially concentrated extract,and wherein the combined hydrocarbon solvent extract is then evaporatedto dryness at temperatures below 40° C., thereby providing themetal-organo complex product.
 24. The method of claim 22 wherein thealiphatic hydrocarbon added to the extract is selected from the groupconsisting of pentane, octane and hexane. .Iadd.
 25. A metal-organocomplex having the structural formula ##STR3## and giving the infraredspectrum represented by the upper curve of the accompanying drawing andgiving the X-ray diffraction data shown in the herein table of Braggspacing and relative intensity. .Iaddend. .Iadd. The metal-organocomplex of claim 25 containing tetrahydrofuran adduct and giving theinfrared spectrum represented by the lower curve of the accompanyingdrawing. .Iaddend. .Iadd.
 27. A method for preparing a metal-organocomplex having at least one sterically exposed metal-metal bond havingthe structure:

    R.sub.n M  M'R.sub.n

wherein R represents the cyclopentadienyl ligand; n is an integer offrom 1 to 3; M and M' each represent the same or a different transitionmetal selected from the group consisting of titanium, zirconium,hafnium, molybdenum and tungsten; and the symbol represents a single ormultiple, sterically exposed metal-metal bond, which comprises: (a)admixing a halogenide of the metal-organo compound selected to supplythe desired ligand, with a cold substantially dry, oxygen-free etherealsolvent solution of potassium, sodium or lithium naphthalene at atemperature between -200° C. and -25° C. in a reaction vessel from whichair or oxygen has been removed or replaced with an inert atmosphere, andagitating the mixture for at least 2 hours; (b) gradually warming thereaction mixture during a period of at least one hour to substantiallyambient temperature; (c) removing the ethereal solvent and excessnaphthalene at temperatures under 40° C.; and (d) extracting the residueat a temperature not exceeding 40° C. to obtain the metal-organocomplex. .Iaddend.